63 light years away in the constellation of Vulpecula lies HD 189733b, a planet similar to Jupiter but slightly larger, slightly hotter, and about the color of Neptune. Based on Hubble spectroscopy data, astronomers figured out six years ago that it contains high amounts of the chemical compound methane, which is often given off as a waste product by living organisms.
You probably didn’t hear much about this at the time, and It wasn’t a coverup; it’s just that a Jupiter-like planet is highly unlikely to harbor life to begin with, and when you factor in the fact that this planet has a surface temperature of about 2000°F/1090°C and a core temperature that may actually be higher, it seems reasonable to assume that the methane came about through natural non-living processes, as methane sometimes does.
John Grotzinger of the Mars Science Laboratory explains both the significance and relative unreliability of methane here:
Still, though: if HD 189733b had been a rocky planet in the habitable zone of a star, it would have been reasonable to conclude that the discovery of methane may have indicated the presence of extraterrestrial life. Methane and oxygen dimers are the two key biosignatures that astronomers currently rely on in determining whether an exoplanet is likely to harbor life.
Earlier this month, an international team led by University College London’s Sergei Yurchenko announced a more comprehensive and sophisticated method for detecting methane on faraway worlds, increasing the odds that—once the James Webb Space Telescope (JWST) is launched in 2018—astronomers will be able to quickly search the 961 exoplanets identified by the Kepler Space Telescope for traces of methane. If we find it, that will lead to more uncertain but encouraging possibilities—more near-discoveries that will give us the hope we want, but not the hard evidence we need.